Power converter for a solar panel

ABSTRACT

A solar array power generation system includes a solar array electrically connected to a control system. The solar array has a plurality of solar modules, each module having at least one DC/DC converter for converting the raw panel output to an optimized high voltage, low current output. In a further embodiment, each DC/DC converter requires a signal to enable power output of the solar modules.

1. FIELD OF THE INVENTION

The subject disclosure relates to systems for utilizing power generatedby solar panels, and more particularly to an improved system forconverting the power generated by a solar panel to improve safety andefficiency.

2. BACKGROUND OF THE RELATED ART

In the modern world, the needs for electrical power are ubiquitous.However, many of the sources of electrical power such as nuclear energyand coal or fossil fuel power generation plants are not always feasible,and generate not only power but excessive pollution, exhaustion ofresources and controversy. In an effort to avoid these drawbacks byutilizing the renewable energy of the sun, photovoltaic solar panelarrays are finding expanded use in the home environment and industry.Solar panel arrays are particularly well-suited to stand aloneapplications in isolated regions. Solar panel arrays not only functionas an alternate energy source but excess power can be sold back toutility companies or stored for later use.

Referring to FIG. 1, a conventional home system is referred to generallyby the reference numeral 10. The system 10 includes a solar panel arrayor solar array 20 mounted on a roof 22 and electrically connected to acontrol system 40. By mounting the solar array 20 on the roof 22, amaximum amount of sunlight, represented by arrows 24, withoutinterference from trees, buildings or other obstructions is more likely.The control system 40 is typically stored within the basement of thehouse, and provides power to the load 26. The load 26 may also receivepower from the utility grid 28 in a conventional manner.

The solar array 20 has a plurality of solar modules 30 a-n which arecomprised of a number of solar cells. Depending on the number of modules30 a-n, the system 10 can have a capacity from a few kilowatts to ahundred kilowatts or more. Typically, the number of modules is somewhatmatched to meet the demands of the load because each module 30represents a significant investment. Moreover, the roof 22 has limitedarea for conveniently and practically retaining the modules 30.Commonly, a module 30 consists of 36 photovoltaic cells which produce anopen circuit voltage (OCV) of 21 to 23 VDC and a max power point voltageof 15 to 17 VDC. Standard power ratings for the solar modules 30 rangefrom 50 W to 150 W. Thus, for an exemplary system 10, where twokilowatts are desired, as many as forty modules 30 may be needed.

For the most part, the prior art solar modules 30 are somewhat limitedby their performance characteristics. In view of this, attempts havebeen made to optimize the solar module usage so that fewer solar modules30 or less space are required. Tracking mechanisms have been added toactively orient each solar module 30 so that the incident sunlight isnormal to the solar module 30 for increased efficiency. Other attemptsat increasing efficiency and applicability of roof mounted solar arrays20 have involved creating turrets to reduce the footprint thereof.Despite these attempts, solar arrays 20 are still uncommon andunderutilized because of the additional expense and complexity thesemethods provide. As a result, the drawbacks of capacity and expense needto be overcome otherwise the range of practical applications for powerfrom a solar arrays 20 will continue to be limited.

A common method for mounting a solar array 20 on the roof 22 is to mounteach solar panel 30 individually and directly onto the surface of theroof 22. This method usually involves the installers carrying each solarpanel 30 up to the roof and mounting them one at a time. Usually, thesolar modules 30 are put into groups to form panels which, in turn, canbe used to form the solar array 20. Solar modules 30 are live, i.e.outputting power, during installation. On a sunny day, the powergeneration can pose a safety hazard to the installers. There is a need,therefore, for an improved solar module control system which forces animproved module into a default off mode with no power output when not inuse. Thus, adequate safety can be assured during installation and atother times of disconnection such as during replacement and repair.

Referring still to FIG. 1, an electrical conduit or conduits (not shown)carry the wiring that electrically interconnects the solar array 20 withthe control system 40. The power output of each module 30 is carriedindividually to a string combiner 42 within the control system 40.Typically, the electrical conduit carries the outputs of the solar array20 in a low voltage, high current bundle. As the size of the solar,array 20 increases, the thickness of the bundle and, in turn, theelectrical conduit increases. As a result, the elect conduit is not onlyunsightly but represents significant danger if exposed. Thus, there is aneed for a solar panel array which provides a high voltage and lowcurrent output that can be carried in relatively small cables which posea minimal safety risk.

The control system 40 includes a central inverter 44 for changing theraw power from the string combiner 42 into usable power for the load 26.The central inverter 44 includes a matching DC/DC converter 46 and anAC/DC converter 48. An optional battery 50 is also shown disposedbetween the matching DC/DC converter 46 and the AC/DC converter 48 foruse in an off grid system or as part of an uninterruptible power supply(hereinafter “UPS”). The matching converter 46 drops the raw solar arraypower down from the string combiner 42 to a desired level. When abattery 50 is used, the typical desired level of voltage is 54V. Thus,the power generated by the solar array 20 may be stored in the batteryfor use during the night or fed to the AC/DC converter 48 for use by theload 26 or sale via the utility grid 28. The AC/DC converter 48 receivesthe 54 VDC power and outputs an AC current at a desired voltage andfrequency such as for example 120, 208 or 240 VAC at 50 or 60 Hz.Converters 46, 48 are well known to those of ordinary skill in thepertinent art and, therefore, not further described herein.

The matching converter 46 may also include maximum power point tracking(hereinafter “MPPT”) for varying the electrical operating point so thatthe solar array 20 delivers the maximum available power. This and othertechniques for effectively using power generated by solar arrays arecommon. An example is illustrated in U.S. Pat. No. 6,046,919 toMadenokouji et al. and is incorporated herein by reference. From theforegoing, it may be observed that the MPPT optimizes the solar array 20as a monolithic unit.

In actuality, the solar array 20 is made up of solar modules 30 thateach typically includes thirty-two cells divided into two groups ofsixteen. Each of the solar module cells and solar modules 30 may be fromdifferent manufacturers and have varied performance characteristics.Moreover, shading by clouds and the like varies the output from cell tocell and module 30 to module 30. Thus, significant improvements in theefficiencies of the solar panels 30 can be realized if each solar module30 can be operated at peak power levels. Similarly, each group ofsixteen cells or even each cell's performance can be enhanced bycorresponding optimization. Such performance would permit solar arrayswith less panels to reduce the cost of a given installation and broadenthe range of practical applications for solar power. There is a need,therefore, for a cost effective and simple control system which cangreatly increase efficiency in new and existing solar arrays.

Further, the typical solar array 20 has a variable output not onlythroughout the day but the output voltage also varies according to otherparameters such as temperature. As a result, the central inverter 44 isalso required to be a variable regulator to control these variations. Inthe United States, galvanic isolation is required for connection to theutility grid 28. The galvanic isolation is usually achieved by a 60 Hztransformer on the output of the central inverter 44. These prior artnecessities further increase the cost and complexity of the controlsystem 40. A solar array which does not need the central inverter 44 toact as a variable regulator or galvanic isolation would advantageouslyreduce the cost and complexity of the control system.

Further still, solar arrays 20 that are configured for grid connect only(without UPS function available) operate only while the utility grid 28is on. In a problematic manner, if a utility grid outage occurs, thepower generated by the solar array 20 cannot be accessed to run the load26. Even for periodic outages lasting for only seconds, requirements aresuch that the solar array 20 cannot be reconnected for five minutesafter the utility grid power has returned. Thus, a need exists for asolar array control unit which can supply power to the load even when autility grid outage occurs.

3. SUMMARY OF THE INVENTION

The present invention is directed to a control unit for controlling anoutput of a solar module. The control unit includes a converter forcoupling to the output of the solar module, the converter beingconfigured and arranged to convert the output to a high voltage and lowcurrent.

It would be desirable to provide a solar array with increased capacity,for a given size, while reducing the complexity and expense so thatsolar power may be used more economically and for a wider range ofapplications.

It would be desirable to provide a solar panel array which optimizes thepower output at a subcomponent level to increase the overall powergenerated.

It would be desirable to provide a control system for a solar arraywhich can be retrofit onto existing arrays to provide increased powergeneration.

It would be desirable to provide a control system for a solar panelwhich defaults in an off mode for allowing safe installation.

It would be desirable to provide a control system which allows forutilization of the power generated by a solar array even when the gridpower is down.

It would be desirable to provide a simplified control system whichutilizes standard, off-the-shelf components. It would further bedesirable to provide an inverter that is standard. In a furtherembodiment, the inverter would also provide galvanic isolation from theutility grid.

It would be desirable to provide a solar array which produces power at arelatively high voltage and low current to allow for relatively smallcables to carry the power in a safe and convenient manner. It wouldfurther be desirable for the solar array power to be at a desirable DCvoltage to allow use of off-the-shelf components. In one embodiment, acontrol unit controls an output of a solar device. The control unitincludes a converter coupled to the output of the solar device such thatthe solar device output is converted to a high voltage and low current.Preferably, the high voltage is between approximately 200 and 600 VDCand the solar device is selected from the group consisting of a solarmodule, a group of solar cells and a solar cell. The converter alsopreferably includes MPPT.

Still another embodiment is directed to a control unit for a solarmodule in a solar array for maximizing the output of the solar module.The control unit includes a converter for coupling to the cells of thesolar module and, thereby, maximize a power output of each cell.

Yet still another embodiment is a solar module array including aplurality of solar modules connected in parallel and a low voltage tohigh voltage DC/DC converter coupled to each solar module for maximizinga power output by each respective module. Preferably, the solar modulearray also includes a DC/AC inverter coupled to an output of the DC/DCconverters for outputting a usable power to a load.

It should be appreciated that the present invention can be implementedand utilized in numerous ways, including without limitation as aprocess, an apparatus, a system, a device and a method for applicationsnow known and later developed. These and other unique features of thesystem disclosed herein will become more readily apparent from thefollowing description and the accompanying drawings.

4. BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the disclosedsystem appertains will more readily understand how to make and use thesame, reference may be had to the drawings wherein:

FIG. 1 is a schematic diagram of a conventional solar panel arrayinstallation;

FIG. 2 is a schematic diagram of a solar panel array installationconstructed in accordance with the subject disclosure; and

FIG. 3 is a schematic diagram of another solar panel array installationconstructed in accordance with the subject disclosure.

5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention overcomes many of the prior art problemsassociated with solar arrays. The advantages, and other features of thesystems and methods disclosed herein, will become more readily apparentto those having ordinary skill in the art from the following detaileddescription of certain preferred embodiments taken in conjunction withthe drawings which set forth representative embodiments of the presentinvention and wherein like reference numerals identify similarstructural elements.

Referring to FIG. 2, an improved solar array power generation system isreferred to generally by the reference numeral 110. As will beappreciated by those of ordinary skill in the pertinent art, the system110 utilizes some similar components as the system 10 described above.Accordingly, like reference numerals preceded by the numeral “1” areused to indicate like elements whenever possible. The system 110includes a roof mounted solar array 120 electrically connected to acontrol system 140. The solar array 120 has a plurality of solar modules130 a-n. Each solar module 130 a-n has a corresponding DC/DC converter131 a-n for converting the raw panel output to a nominal 400 VDC output.Thus, the modules 130 may be easily connected in parallel and, in turn,connected to the control system 140 by a relatively small, safe, highvoltage, low current cable (not shown). The resulting 400 VDC level ismore suitable for the creation of 120 or 240 VAC than, for example, a 12VDC car battery. Another advantage realizable by use of the converters131 is that relatively high switch frequencies can be employed tosignificantly reduce the size and filtering requirements of the system110.

In a further embodiment, the DC/DC converters 131 include MPPT. TheDC/DC converter 131 with MPPT maximizes the module output according tothe present operating conditions of the solar module 130. For example,module 130 a may be temporarily shaded by a cloud or object while module130 c is receiving direct sunlight. Under such circumstances, theperformance characteristics of panels 130 a and 130 c would bedifferent, e.g., the optimum power settings for each panel would not bethe same. The corresponding DC/DC converters 131 a and 131 c woulduniquely adjust the module's operation such that modules 130 a and 130 cwill produce the maximum power possible individually. Accordingly, themaximum power output of the solar array 120 is maximized and fewermodules 130 may be employed to produce comparable power to prior artsystems.

In a preferred embodiment, each module 130 contains thirty-two cellsdivided into two groups of sixteen. A diode (not shown) is commonlydisposed between each group of sixteen cells to prevent reverse currentflow during shady conditions and other events which may cause variationin panel output. A plurality of DC/DC converters 131 regulate the outputof each group of sixteen cells of the module 130 by picking up theoutput at the diode. Thus, the advantages of the subject disclosure maybe utilized in new and existing solar modules by retrofit. In stillanother embodiment, the DC/DC converters 131 are connected to maximizethe output of each cell of the module 130.

In a further embodiment, the DC/DC converters 131 are also configured torequire a signal from the control system 140 to output power. If thepanel 130 is not receiving this signal, then the default mode of nopower output is achieved. Consequently, installers can handle panels 130on a sunny day without concern for the live power generated thereby.

The control system 140 is also improved by further simplification in thepreferred system 110. The control system 140 includes a central inverter144 having a single DC/AC inverter 147. The DC/AC inverter 147 preparesthe raw power from the solar array 120 for use by the load 126 or saleto the utility company via the utility grid 128. In the preferredembodiment, the inverter 147 is a relatively simple, low dynamic range,off-the-shelf high voltage inverter for dropping the voltage down andcreating the desired frequency. Since the DC/DC converters 131 regulatethe power outage from the solar panels 130, the control system 140 canbe optimized for efficiency since a very small input voltage range isrequired for operation. In an embodiment where the solar array 120outputs 400 VDC, a standardized inverter 147 can be used to beneficiallyand significantly reduce the wiring complexity and, thereby, the cost ofthe control system 140. In a further embodiment, galvanic isolation canbe maintained in the standardized inverter 147. Accordingly, the controlsystem 140 is further simplified.

Referring now to FIG. 3, as will be appreciated by those of ordinaryskill in the pertinent art, the system 210 utilizes the same principlesof the system 110 described above. Accordingly, like reference numeralspreceded by the numeral “2” instead of the numeral “1”, are used toindicate like elements. An optional energy storage device 250 isdisposed between the control system 240 and the solar array 220. In oneembodiment, the energy storage device 250 is a high voltage flywheelenergy storage system which ideally operates at 400V. Accordingly, theoutput of the DC/AC inverter 247 is matched to optimize the operatingefficiency of the high voltage flywheel. Acceptable 6 kWh high voltageenergy flywheels are available from Beacon Power Corporation inWilmington, Mass. In another embodiment, the energy storage device 250is a conventional battery.

In still another embodiment, the energy storage device 250 is acapacitor and the system 210 acts as an uninterruptible power supply.The capacitor 250 charges during normal operation as the solar array 220and utility grid 228 provide power to the load 226. In a system with aconventional battery, such operation would shorten the life of thebattery as is known to those of ordinary skill in the pertinent art.However, with a capacitor such short life is avoided.

During an interruption of utility grid power, the capacitor dischargesto provide interim power to the load 226 until an electronic switch (notshown) can be actuated to allow the solar array 220 to meet the demandof the load 226. It is envisioned that the capacitor will be able tomeet the demand for at least twenty seconds although advantages would beprovided by a capacitor with only a few seconds of sustained poweroutput. Thus, the power output from the solar array 220 can still beaccessed even when the utility grid 228 is down. In a furtherembodiment, the capacitor is what is commonly known as anelectro-chemical capacitor or ultra capacitor. The capacitor may be acarbon-carbon configuration, an asymmetrical carbon-nickel configurationor any suitable capacitor now known or later developed. An acceptablenominal 48V, 107F ultra capacitor is available from ESMA of the TroitskMoscow Region in Russia, under model no. 30EC104U.

In another embodiment, an alternative energy source such as aconventional fuel burning generator, fuel cell or other suitablealternative acts as a backup in combination with a solar array.

While the invention has been described with respect to preferredembodiments, those skilled in the art will readily appreciate thatvarious changes and/or modifications can be made to the inventionwithout departing from the spirit or scope of the invention as definedby the appended claims.

1. A system comprising: a plurality of solar units, each solar unit ofthe solar units comprising: a solar generator having at least one solarcell to generate electric power; only one pair of output connections toprovide output; and a DC/DC converter coupled between the solargenerator and the pair of output connections to receive electricityprovided by the solar generator in entirety and to provide the outputvia the pair of output connections, wherein the DC/DC converter isconfigured to operate the solar generator at a maximum power pointindependent of other solar units of the plurality of solar units; agalvanically isolated output inverter; and a set of wires configured toconnect output connections of the solar units and the galvanicallyisolated output inverter in series; wherein the DC/DC converter isconfigured to employ a switching frequency for transferring electricityfrom the solar generator to the series connection of the solar unitsestablished by the set of wires.
 2. The system of claim 1, wherein thegalvanically isolated output inverter comprises an output inductor,wherein the set of wires is configured to connect the output connectionsof the solar units and the output inductor in series.
 3. The system ofclaim 1, wherein when the DC/DC converter is switched on, the solargenerator is connected in the series connection of the solar unitsestablished by the set of wires; and wherein when the DC/DC converter isswitched off, the solar generator is electronically disconnected fromthe series connection.
 4. The system of claim 1, wherein the DC/DCconverter includes a switch, and an energy storage capacitor coupledbetween the solar generator and the switch; wherein when the DC/DCconverter is switched on, the solar generator and the energy storagecapacitor are connected in parallel and further connected in the seriesconnection of the solar units established by the set of wires; andwherein when the DC/DC converter is switched off, the solar generator iselectronically disconnected from the series connection.
 5. The system ofclaim 1, wherein the DC/DC converter includes a switch, and an energystorage capacitor coupled between the solar generator and the switch;wherein when the switch is turned on, the solar generator and the energystorage capacitor are connected in parallel and further connected in theseries connection of the solar units established by the set of wires;and wherein when the switch is turned off, the solar generator and theenergy storage capacitor are electronically disconnected from the seriesconnection.
 6. The system of claim 1, wherein when the DC/DC converteris switched on, the solar generator is connected in the seriesconnection of the solar units established by the set of wires; andwherein when the DC/DC converter is switched off, the solar generator iselectronically disconnected from the series connection.
 7. The system ofclaim 1, wherein the DC/DC converter includes a switch, and an energystorage capacitor coupled between the solar generator and the switch;wherein when the DC/DC converter is switched on, the solar generator andthe energy storage capacitor are connected in parallel and furtherconnected in the series connection of the solar units established by theset of wires; and wherein when the DC/DC converter is switched off, thesolar generator is electronically disconnected from the seriesconnection.
 8. The system of claim 1, wherein the DC/DC converterincludes a switch, and an energy storage capacitor coupled between thesolar generator and the switch; wherein when the switch is turned on,the solar generator and the energy storage capacitor are connected inparallel and further connected in the series connection of the solarunits established by the set of wires; and wherein when the switch isturned off, the solar generator and the energy storage capacitor areelectronically disconnected from the series connection.
 9. The system ofclaim 1, further comprising a controller configured to operate the solargenerator at a maximum power point independent of other solar units ofthe plurality of solar units.
 10. The system of claim 9, wherein theDC/DC converter comprises the controller.
 11. The system of claim 2,further comprising a controller configured to operate the solargenerator at a maximum power point independent of other solar units ofthe plurality of solar units.
 12. The system of claim 11, wherein theDC/DC converter comprises the controller.
 13. The system of claim 1,wherein the set of wires is configured to filter electricity receivedfrom the series connection of the solar units.
 14. The system of claim1, wherein the system is configured to filter electricity received fromthe series connection of the solar units.
 15. The system of claim 1,wherein the system is configured for filtering.
 16. The system of claim1, wherein the system is configured for filtering electricity.
 17. Thesystem of claim 1, further comprising a central control systemconfigured to generate a control signal, wherein each of the DC/DC powerconverters is configured to vary a respective DC/DC power converter'smode of operation in response to receiving the control signal.
 18. Thesystem of claim 1, further comprising an energy storage device, whereinthe set of wires is configured to connect the output connections of thesolar units and the energy storage device.
 19. A method, comprising:connecting outputs of a plurality of solar units in series to form aseries connection, wherein each of the solar units comprises a solargenerator having at least one solar cell to generate electric power, anda DC/DC converter coupled with the solar generator to receive theelectric power generated by the solar generator in entirety andconfigured to output the electric power through the plurality of solarunits connected in series, wherein the DC/DC converter is configured toemploy a switching frequency for transferring electric power from thesolar generator to; wherein when the DC/DC converter is switched on, thesolar generator is connected in the series connection in the pluralityof solar units; wherein when the DC/DC converter is switched off, thesolar generator is electronically disconnected from the seriesconnection; and controlling the DC/DC converter of each of the solarunits to operate a respective solar generator at a maximum power pointindependent of other solar units of the plurality of solar units thatare connected in series.
 20. A method, comprising: generatingelectricity in direct current (DC) using a solar generator; andoperating a converter coupled between the solar generator and a seriesconnection of solar generators to allow the solar generator to supply afirst current to the series connection of solar generators, wherein theconverter is controlled to operate the solar generator at a maximumpower point independent of other solar generators in the seriesconnection of solar generators; wherein the converter is configured toallow a second current larger than the first current to flow through theseries connection of solar generators; wherein when the converter isswitched on, the solar generator provides the first current to theseries connection of solar generators, and the second current is equalto or larger than the first current; and wherein, when the converter isswitched off, the solar generator is electronically disconnected fromthe series connection of solar generators.